1. Field of the Invention
The present invention relates to a receiver device and method for receiving radio signals through at least two receiving paths, e.g. through different/many sector antennas of a base station device.
2. Description of the Prior Art
In cellular communication networks, one way of improving uplink coverage is to increase the number of receiving antennas at a base station. The selection of the particular antenna configuration may depend, for example, on the radio channel characteristics, angular spread, mobile speeds, uplink and downlink capacities, implementation complexity, environmental issues, visual impact of the antennas, network provider's cost/quality of service model, etc.
In a conventional arrangement, each cell is divided into typically three sectors and the base station employs two directional antennas per sector. Each antenna pattern covers the entire sector. Receive diversity is usually applied in the uplink direction (that is from mobile terminal device or user equipment to the base station), while often only one of the two antennas is used for downlink transmission. In receive diversity, a signal is received through both directional antennas in each sector and the antenna with the better reception quality (for example, signal-to-noise ratio or the like) is selected. Thus, receive or antenna diversity leads to an improved base station reception sensitivity. Many methods of maximizing signal quality are available.
FIG. 1 shows a schematic diagram indicating an antenna arrangement 20 with a plurality of isotropic antenna elements 22 arranged in a triangular structure. The antenna arrangement 20 is connected to a base transceiver station 30, which transmits and receives signals using the antenna arrangement 20.
FIG. 2 shows an ideal antenna pattern of the antenna arrangement 20, which comprises three sectors 10 each covering an angular range of about 120 degrees. Each of the sectors of the antenna pattern is mainly generated by those antenna elements 22 that are arranged on the respective side of the triangular structure. However, the real antenna pattern sectors are non-ideal in several ways. There is a non-negligible power radiated in the back and side regions, and the amount of such back and side power generated by back and side lobes 14 is greater for narrow sectors than the amount of power for wide-angle sectors. Back and side lobes generate co-channel interferences. Thus, the number of sectors is selected based on frequency re-use and allowed channel interference.
In the example of the above tri-sector base station configuration with an employed two-antenna receive diversity, each sector 10 may have four transmitter units for downlink transmission through four respective channels, leading to a total of twelve transmitter units per base transceiver station (BTS). To implement receive diversity, each sector 10 requires eight receiver units, four allocated to the four channels of the first or main antenna and another four allocated to the four channels of the second or diverse antenna. Thus, a total of twenty-four receiver units would be required for implementing such a base station configuration.
To alleviate this problem, a new technology, known as multi-carrier technology has been developed, where multiple parallel narrowband carriers are used for parallel transmission and reception of the channel signals of a sector antenna by respective single transmitter and receiver units, respectively. Thus, the number of transmitter and receiver units can be reduced down to two receiver units and one transmitter unit per sector 10. This results in a total of three transmitter units per BTS and six receiver units per BTS.